Heretofore, L-glutamic acid has been produced by a fermentation method using mainly so-called a coryneform L-glutamic acid producing bacterium belonging to the genus Brevibacterium, Corynebacterium or Microbacterium or a variant thereof (Amino Acid Fermentation, Gakkai Shuppan Center, pp. 195-215, 1986). Known processes for producing L-glutamic acid by a fermentation method using other strains include one using a microorganism belonging to the genus Bacillus, Streptomyces or Penicillium (U.S. Pat. No. 3,220,929), one using a microorganism belonging to the genus Pseudomonas, Arthrobacter, Serratia or Candida (U.S. Pat. No. 3,563,857), one using a microorganism such as a bacterium belonging to the genus Bacillus, Pseudomonas, Serratia or Aerobacter aerogenes (currently Enterobacter aerogenes) (Examined Japanese Patent Publication No. 32-9393), one using a mutant of Escherichia coli (Japanese Laid-open Patent Application No. 5-244970) and the like.
The productivity of L-glutamic acid has been considerably improved by the breeding of the above microorganisms or the improvement of the production processes. To meet growing demand for L-glutamic acid, the development of a more inexpensive and efficient process for producing L-glutamic acid is desired.
In view of the above situation, the inventors of the present invention has investigated and studied microorganisms having L-glutamic acid productivity broadly. As a result, it has been found that a microorganism having high L-glutamic acid productivity can be obtained by increasing the activity of an enzyme which catalyzes the L-glutamic acid biosynthesis reaction (citrate synthase, phosphoenolpyruvate carboxylase, glutamate dehydrogenase) of a microorganism belonging to the genus Enterobacter, Serratia, Klebsiella or Erwinia (Japanese Laid-open Patent Application Nos. 10-224909 and 10-297129).
The inventors have also found that a microorganism having high L-glutamic acid productivity is obtained by enhancing the activity of each of these enzymes by introducing a gene coding citrate synthase (hereinafter sometimes abbreviated as “CS”) and phosphoenolpyruvate carboxylase derived from the genus Escherichia into a valine sensitive strain belonging to the genus Escherichia (WO 97/08294).
Meanwhile, it has been reported that the introduction of a gene (CS gene) coding citrate synthase derived from Escherichia coli or Corynebacterium glutamicum is effective in improving the L-glutamic acid productivity of Corynebacterium or Brevibacterium (Examined Japanese Patent Publication No. 7-121228). When these coryneform bacteria were used as a host, the introduction of a CS gene derived from Corynebacterium glutamicum of the same species as the host showed a slightly higher effect than the introduction of a CS gene derived from Escherichia coli but there was not seen a marked difference between them.
As described above, it has been known that a CS gene is introduced into various microorganisms to improve L-glutamic acid productivity. However, there has not been known an example where a CS gene derived from a coryneform bacterium is introduced into a microorganism belonging to enterobacteria such as a bacterium belonging to the genus Escherichia. 